The present invention relates to a constant airflow control apparatus which is disposed inside a duct of an air conditioning system and automatically adjusts the flow rate of air fed through the duct into a room to keep the air supply constant.
In an air conditioning system installed in a building, branch ducts connected to the main duct of a central air conditioner are distributed to different floors or rooms. Air from the central air conditioner is supplied to the rooms through discharge ports of the branch ducts. In an air conditioning system of this type, if the flow rate of the air is adjusted to the conditions of one room, operation of the discharge ports or change of the airflow rate in other rooms will cause variation of air pressure in the main and branch ducts, resulting in variation of the airflow rate in one room. In order to avoid such an awkward situation, each branch duct is conventionally fitted with a constant airflow control apparatus which automatically keeps the flow rate of supplied air constant even though the air pressure inside the duct varies.
One such prior art constant airflow control apparatus is disclosed in Japanese Patent Publication No. 35615/80. In this constant airflow control apparatus, a movable shaft is provided inside a case which is in the form of a rectangular tube. A pair of guide plates are hinged on one end of the movable shaft. Pressure receiving plates are individually hinged on both ends of the guide plates. Both ends of the pressure receiving plates are hinged on a bearing member for supporting the movable shaft.
This constant airflow control apparatus is so designed that a constant airflow rate is maintained on the basis of the balance between the spreading action of the two pressure receiving plates and the restoring force of a spring to compensate variations of air pressure.
In the prior art constant airflow control apparatus described above, however, the guide plates and the pressure receiving plates are coupled into a substantially rhombic configuration, so that the guide plates require a long traveling stroke. Also, the rhombic structure moves pantographically, and can extend over a long distance in the axial direction of the movable shaft. Thus, the apparatus is increased overall in length and in weight.
Moreover, the guide plates are hinged on the movable shaft, which is supported by bearings at the front and rear end portions thereof. Therefore, the slide guide portions are concentrated on the central axis of the casing, so that the weights of all of the guide plates and the pressure receiving plates are exerted on the slide guide portions, increasing friction. Further, the whole moving part is liable to be tilted by a deflected flow of incoming air, so that biased load acts on the slide guide portions to cause scuffing. Thus, the prior art constant airflow control apparatus lacks in reliability in operation under low pressure or under the influence of a deflected airflow.